King County, WA
Septic system inspections in King County
Updated · Editorial team; not yet technically reviewed
Short answer
In King County, state code enforced by Public Health – Seattle & King County requires conventional gravity septic systems to be inspected every 3 years, and pressure distribution, mound and sand filter systems every year. A licensed on-site system maintainer inspects the tanks, distribution and drain field and reports the results to Public Health.
What King County handles
Conventional gravity septic systems must be inspected every 3 years under state code enforced by Public Health – Seattle & King County. [1]
Pressure distribution, mound and sand filter systems must be inspected every year. [1]
The maintainer inspects septic and pump tanks, any treatment component, the distribution system, and the drain field and reserve areas, then reports to Public Health. [1]
Which system do you have?
Newer and rural lots often have pressure distribution or mound systems, used where a gravity drain field can't treat sewage safely for the life of the home. They have pumps, controls and alarms, which is why they're checked yearly. Your permit record or as-built drawing names the type.
Between inspections
- Keep food waste out of the drain; compost or trash it.
- Spread laundry loads across the week.
- Don't drive or park on the drain field or reserve area.
- Fix running toilets and leaks right away; extra water overloads a field. See toilet repair.
If a pump alarm sounds
On a pressure or mound system, an alarm usually means the pump chamber is filling. Cut water use to a minimum and call your maintainer; ignoring it can flood the tank and back sewage into the house.
Further reading: How sewer camera inspections work.
City-specific guides in King County
Common questions
How often must a King County gravity septic system be inspected?
Every 3 years.
How often are King County mound and pressure systems inspected?
Every year, as are sand filter systems.
Who inspects a septic system in King County?
A licensed on-site system maintainer, who reports results to Public Health – Seattle & King County.
What does a King County septic inspection cover?
Septic and pump tanks, any treatment component, the distribution system, and the drain field and reserve area.
Why do mound systems need yearly inspection in King County?
They use pumps, controls and alarms, and serve lots where a gravity field couldn't treat sewage reliably.
What should I do if my septic alarm goes off?
Use as little water as possible and call your maintainer before the tank overfills.
Can I park on my drain field?
No. Vehicles compact the soil and can crush pipes in the field and reserve area.
Does food waste hurt a septic system?
Yes. Public Health advises putting food waste in compost or trash instead of the drain.
How do I find what type of septic system I have in King County?
Check the permit record or as-built drawing for the property.
Do Seattle homes need septic inspections?
Homes on city sewer don't; the rules apply to properties on on-site systems.
Cities and services in King County
Sources (1)
- Public Health – Seattle & King County, On-site sewage system inspections · checked 2026-10-03